Refractive index is one of the important optical parameters. A new simple experimental instrument is designed by using polarized light experimental instrument ( WPZ type) stand，light source，and a diameter of 6 cm 200 ml glass beaker which of 60 × 80 × 2 ( mm3 ) rectangular transparent glass is in the middle，madding it be separated into the two parts. The refractive index of any kind of transparent liquid is measured according to the total reflection law of light. And the refractive index of distilled water，saturated sucrose and diiodomethane was measured by this method. The experimental results show that this method has the advantages of easy operation，low cost and high efficiency，and has certain reference value for the measurement of refractive index of transparent liquid.